Fog Light Installation Help

The way I see it, you are not going to be able to avoid running the wires through the firewall. As noted in the doc, you will see where you can do that. Two wires were needed, a power in wire (tapped from the fuse box under the hood and out power from the relay to the lamp harness).
As also noted in the doc, the relay can be stuffed under the upper left hand of the dash where there is a brown wire leading into a ECU. This wire is hot when the parking / headlights are turned on.
I used the entire harness that came with the light kit. The only tap I had to do was into that brown wire mentioned above.
No warning for burned out lights.

 

I placed the relay and fuse behind the upper left hand side of the dash next to the ECU that had the brown wire, yes. The two wires I ran through the firewall.

 

You don't need to go through the firewall.

You need a 12V relay inside the engine compartment that will switch in the high-current power for the fog lights (which you can tap into at the engine compartment fuse block, using a wire with an in-line fuse). The "control" for this relay (the power going to its coil) will come from tapping into either the low beam or parking light line (12V side, not ground) inside the engine compartment. You don't need any other switch or control. The small amount of current the relay's coil will draw will pose no threat to the existing light wiring. You do need to be careful about the high-current line(s) to the fog lights themselves, though. They should be at least 16 ga each. Some have tapped into the fuse box at an unmarked lug in the fuse box - there are photos in the post - I'm not sure what that lug is for, or how much current it can handle, but I suspect it's probably OK.

You will get no dash warning if the fogs go out.

 

Thanks for pointing out this alternative jayvee.
The only downside to this wiring configuration is that you won't be able to turn off the fogs if the parking/headlights are on. For me I like to shut the lights off as I am going up the parking garage so the engine won't have to come on to charge the battery.

 

I have 2010 Prius IV and am interested in installing fog lights as well. Can you tell me precisely which fog lights you purchased and from where so that I'm certain they'll work and of course fit the factory fog lamp covers.

Thanks.